What is final and harmonious solution to arrive at between any countries ?

If war is the solution , that in the history we have seen that with the war only the boundries change that too for some time.
Again after that the hate among countries increase till there is world order is changed by re alignment ...this keeps on happening for every 100 years

We call man a thinker and better than animals ...but history shows otherwise

Countries do not function the same way persons do - a country (or its people) needs something to gain from another to treat it as a friend.

In western Europe after the second world war, integraton of countries was considered the way to lasting peace. It has worked pretty good between former enemies like Germany, France and UK - and even after Brexit, war is not expected to come between those countries.

This integration was economic foremost. When one country depends on another economically, and such interests are complex enough, the economic system that those countries are constituents of, becomes "too large to fail" - and war (in traditional sense anyway) becomes impossibility.

Why this does not work globally, is that many countries are so different from each other. Western European countries are pretty much the same socially and economically, so their integration would have been relatively easy - still even the EU crackles on some of the border states in east and south (which results on UK's decision to exit for example).

One specific detail is that these countries have pretty solid ratio of GDP coming from domestic consumption and services. Investors from France can plug in the industry in Germany, and that would make French aggression toward Germany a financial loss for those investors in France - and because the leaders in France are democratically elected, they have to listen to those French who have investments abroad (while also listening to those who do not).

In countries that depend heavily on exports (most oil-rich countries) or have very different system of governance s from their neighbours (China or DPRK for example), economic integration with their neighbours is not so straightforward.

But regardless, I think that most effective way to build lasting peace is to develop the world in direction where individuals in country A have something to gain by continuing and improving well-being of individuals in country B, and vice versa.

If we reflect that point of view on cold war period for example - "western" citizens and their leaders generally did not see much improvement in well-being of individuals in Soviet Union under communist rule, and that certainly was factor behind much of the malcontent or war-mongering on their side.